Gulf of Maine Seasonal Sea Surface Temperature Update
Seasonal Patterns in Sea Surface Temperatures
About the Updates:
Over the past decade, scientists at the Gulf of Maine Research Institute have led a body of research that highlights the rapid pace of warming in the Gulf of Maine. To keep you informed, we share seasonal updates about conditions in the Gulf of Maine.
Note About the Data: The figures in this report are created using remotely-sensed satellite data as part of publicly funded research efforts. Satellite SST data was obtained from NOAA’s National Center for Environmental Information (NCEI), with all maps and figures displaying NOAA’s Optimum Interpolation Sea Surface Temperature Data.
The Gulf of Maine Region
For analyses like these, it is important to be clear about the spatial extent that “defines” the Gulf of Maine (Figure 1), as different borders could produce different results. The spatial domain we use as the “Gulf of Maine” is displayed below. This area is consistent with previous seasonal and annual Gulf of Mainereports GMRI has produced.
Season Highlights
For this seasonal report we present an analysis of SST for spring (March 1st, 2023 - May 31st, 2023). During this season, the average SST for the Gulf of Maine was 45.72°F, making it the 2nd hottest spring on record for the period of 1982-2023 — the period over which the satellite data used are available. This seasonal average temperature is 2.88°F above the 1991–2020 CRP spring average of 42.84°F.
Weekly Temperatures
In (Table 1), we highlight how the SST for each week this spring compares to the 30-year CRP period (i.e., climatological averages from 1991 through 2020) for the area shown in Figure 1.
The observed SST, long-term average SST trends, and SST anomalies (i.e., departures from the long-term average SST) are shown. Departures from the long-term average were 2°F or more above normal during March & April, with temperatures in May falling closest to the long-term average.
| Weekly Sea Surface Temperatures - Spring | ||||||
| (March 1st, 2023 - May 31st, 2023) | ||||||
| One-Week Period | Observed Temperature | Climatological Average | Temperature Anomaly | |||
|---|---|---|---|---|---|---|
| °F | °C | °F | °C | °F | °C | |
| Mar 01 - Mar 04 | 44.10 | 6.71 | 40.10 | 4.50 | 3.99 | 2.21 |
| Mar 05 - Mar 11 | 43.90 | 6.60 | 40.00 | 4.45 | 3.89 | 2.16 |
| Mar 12 - Mar 18 | 44.70 | 7.04 | 40.00 | 4.44 | 4.68 | 2.60 |
| Mar 19 - Mar 25 | 43.10 | 6.16 | 40.10 | 4.50 | 2.99 | 1.66 |
| Mar 26 - Apr 01 | 43.00 | 6.10 | 40.30 | 4.63 | 2.63 | 1.46 |
| Apr 02 - Apr 08 | 44.50 | 6.92 | 40.80 | 4.86 | 3.71 | 2.06 |
| Apr 09 - Apr 15 | 45.20 | 7.33 | 41.30 | 5.19 | 3.84 | 2.14 |
| Apr 16 - Apr 22 | 45.70 | 7.64 | 42.10 | 5.62 | 3.63 | 2.02 |
| Apr 23 - Apr 29 | 45.60 | 7.58 | 43.10 | 6.15 | 2.57 | 1.43 |
| Apr 30 - May 06 | 46.50 | 8.05 | 44.20 | 6.76 | 2.33 | 1.29 |
| May 07 - May 13 | 47.30 | 8.50 | 45.30 | 7.41 | 1.95 | 1.08 |
| May 14 - May 20 | 48.00 | 8.87 | 46.70 | 8.15 | 1.31 | 0.73 |
| May 21 - May 27 | 48.90 | 9.40 | 48.10 | 8.93 | 0.85 | 0.47 |
| May 28 - May 31 | 51.30 | 10.70 | 49.20 | 9.58 | 2.10 | 1.17 |
| Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data. | ||||||
| Climatological Reference Period: 1991-2020. | ||||||
Monthly Statistics
Table 2 shows monthly average SST for 2023, where we see each month was nearly 2°F or more above the 1991-2020 CRP. March showed the largest deviation from the long-term climatological average, with an average SST anomaly of 3.62°F.
| Monthly Sea Surface Temperatures - Spring | |||||||
| (March 1st, 2023 - May 31st, 2023) | |||||||
| All-Year Rank | Observed Temperature | Climatological Average | Temperature Anomaly | ||||
|---|---|---|---|---|---|---|---|
| (1982-2023) | °F | °C | °F | °C | °F | °C | |
| Mar | 1 | 43.70 | 6.51 | 40.10 | 4.50 | 3.62 | 2.01 |
| Apr | 1 | 45.20 | 7.36 | 41.80 | 5.47 | 3.40 | 1.89 |
| May | 6 | 48.20 | 8.99 | 46.50 | 8.08 | 1.64 | 0.91 |
| Data Source: NOAA OISSTv2 Daily Sea Surface Temperature Data. | |||||||
| Climatological Reference Period: 1991-2020. | |||||||
Seasonal Trends and Anomalies in Context
The Gulf of Maine is an area of particular interest to the scientific community because of the remarkable rate of warming it has experienced in recent years coupled with its importance as a major driver for the regional economy.
When looking at average spring temperatures from the beginning of the satellite record in 1982 Figure 2, there is a clear long-term increase, with SST’s warming at a rate of 0.57°F per decade. This rate of seasonal spring warming is ~4x the rate that global ocean temperatures are warming (0.23°F per decade).
The unprecedented levels of warmth over the past decade or so are consistent with what researchers believe has been a distinct regime shift in terms of the major influences on SSTs in the Gulf of Maine. The drivers of this (e.g., a potential weakening of the Atlantic Meridional Overturning Circulation, widening of the Gulf Stream, changes in the characteristics of the Labrador Current) have been well-documented in the peer-reviewed literature, including through research by GMRI scientists.
How Does this Spring Compare?
2023 is the 2nd warmest spring season observed in the Gulf of Maine during the 41 years we have satellite data to analyze. The top 5 warmest spring seasons have all occurred in the last decade.
Marine Heatwave Conditions
The most commonly used definition of a “marine heatwave” (MHW) is when daily average SSTs exceeded the 90th percentile of a climatological (i.e., 30-year) average for at least 5 consecutive days. Gaps of 2 days or less in this threshold do not constitute a break in the MHW event.
Using this broadly accepted definition, the Gulf of Maine has experienced MHW conditions for 71% of this spring. May was the only month this Spring where where SST was below the threshold of a MHW (90th Percentile).
Presenting SST conditions in terms of anomalies (?@fig-season-anoms-rework) as opposed to absolute values (Figure 4) illustrates in greater detail the magnitude of MHW conditions throughout the spring. The most extreme daily SST anomalies occurred in March, with temperatures exceeding 5°F above the climatological average.
Heatmap of Temperature Anomalies and Heatwave Events
Looking at the full record of daily SST anomalies in the Gulf of Maine (Figure 6), the distinct thermal regime shift beginning around 2010 is evident. Indeed, since 2012, the Gulf of Maine has experienced far more persistent MHW conditions (indicated by solid black lines) than at any other point in the satellite record.
The Visual Impact of a New Climate Reference Period
The identification and communication surrounding marine heatwaves is an area of active scientific discussion. Using our heatmap figure (Figure 6) as a visual guide, we can compare what the competing MHW methodologies say is the MHW record for the region. The transition to a full climatological reference period that covers all years (1982-2022) and the removal of the long-term trend brings a focus onto only the most “extreme” events. Using the slider below, we can showcase what a transition from the fixed-baseline methodology used in this report (and previous reporting), to an approach that removes long-term trends.
From this view we can reveal that the transition has removed the majority of marine heatwave events, solving a communication challenge of the “year long heatwave”. By adopting this new method scientists have succeeded in identifying the extreme temperature swings, but there is ongoing debate on when to apply this method, and on some of the unintended consequences of doing so. Among the concerns that scientists have voiced is that this new method retroactively changes the history of past events by accommodating all the more recent (often more extreme) conditions. This makes it difficult to preserve the significance that these events had during their own times.
A second major concern surrounds removing the “trend”, and methodological choices scientists must make to achieve this. This new MHW methodology portrays this step in its simplest form, a linear trend. This structure may not be appropriate across all areas and at varying lengths of temporal coverage. The selection choices of the years to include or exclude and how best to model the observed trends create more “knobs” for practitioners to tune and with them more challenges for clarity of communication. To learn more about these trade-offs and the discussion around Marine Heatwaves, please check out our technical report on the subject.
Spatial Distribution of Seasonal Anomalies
From a spatial perspective, the Gulf of Maine and (most) surrounding areas experienced above average SSTs during spring 2023, but the warmest patches were to the south and east of Georges Bank, mostly outside the domain analyzed in preceding sections. The highest seasonally averaged anomaly of any location above was 6.11°F - along the southern edge of the domain analyzed.
Monthly Temperature Anomalies
Average monthly SST anomalies are shown in Figure 10. The warmest anomalies were observed in March and April and were largely confined to areas just beyond the region of study (i.e, beyond the continental shelf where the Gulf Stream and Labrador Current have significantly more influence on oceanic conditions).
A Note on Data Sources:
NOAA_ERSST_V5 data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.ersst.v5.html.
NOAA High Resolution SST data provided by the NOAA/OAR/ESRL PSL, Boulder, Colorado, USA, from their Web site at https://psl.noaa.gov/data/gridded/data.noaa.oisst.v2.highres.html.
Citing This Work
If you would like to cite this report, please use:
Gulf of Maine Research Institute. 2022. Gulf of Maine Warming Update: Spring 2023